EP1876551A1 - Method for operating a RFID system and reader for a RFID system - Google Patents

Abstract

The method involves recognizing manipulations of a generator signal (GS) produced by the generator (7) for the excitation of the transponder. A read coil signal (MS) received by a read coil (L) of the reading device (2) is compared by a comparison unit (10).

Description

The present invention relates to a method for operating an RFID system according to the preamble of patent claim 1, in which a reading device by means of a generator at least one transponder (tag) wirelessly supplied with electromagnetic energy and in which the transponder transmits data to the reading device, in particular by Modulation of its load characteristics. The load change of the tag causes by retroactivity to the exciter field a load change of the generator, which serves as an evaluation criterion for reading the payload.

Furthermore, the present invention relates to a reader according to the preamble of claim 8 for an RFID system, comprising a exciter or resonant circuit with a transmit / read coil for transmitting and receiving electromagnetic signals and coupled to the exciter or resonant circuit generator for exciting the exciter - Or resonant circuit with a generator signal.

Finally, the present invention relates to an RFID system according to the preamble of claim 15 with at least one reader and a number of transponders, which are supplied by the reader with electromagnetic energy and for transmitting data to the reading device, in particular by load modulation, are formed.

Radio-frequency identification (RFID) systems are also currently gaining in importance for mass deployment. Possible examples of the use of such systems are immobilizers and locking systems for motor vehicles, automatic Feeding systems in animal husbandry, machine-readable passports or the like. However, such systems are relatively expensive and thus not suitable for a mass market. Further, less expensive applications are in the area of automatic supermarket cash registers, where goods are identified and billed via transponders, or access controls with entrance tickets, in which transponders with a limited service life (single use) are used.

In particular, in the context of the latter application examples are regularly passive transponders are used, which are powered by an emitted by the reader electromagnetic field with energy. On the other hand, the resulting electromagnetic coupling of reader and transponder is also used to transmit information from the transponder to the reader. For this purpose, the transponder makes a targeted change in its physical-electrical properties, which is noticeable in the above-described coupling field between reader and transponder as a corresponding signature, which is detected, demodulated and evaluated by the reader.

Since it is to be expected that the RFID technology will prevail on the market in the next few years, for example in the case of tickets, entrance tickets, price tags, inventory control systems or the like, synchronous with such market penetration is also the frequent occurrence of attempted manipulations of such systems to count. If, in fact, it is possible to manipulate the above-outlined communication between the transponder and the reader, unauthorized procurement of goods, services or information is easily possible.

Since it is virtually impossible due to the strong decrease of field strength or coupling between reader and transponder with the relative distance, the communication between a reader and a given transponder by means of a second transponder or RFID tags, it is assumed that a potential attacker is forced to actively intervene by energy supply in the reading process between the reader and transponder. In other words, in the present description it is assumed that a disturber uses an active transmitter which, by generating a high field strength, even at a greater distance from the reading device, is able to dominate the coupling between a transponder and a reading device thus concealing the presence of a transponder to the reader. Furthermore, the attacker can simulate a fake reading information by modulating a transmission power of the jammer the reader.

The invention has for its object to provide a method for operating an RFID system and a suitable for carrying out this method reader, can be reliably detected by the manipulations of the type described above.

According to the invention the object is achieved in a method of the type mentioned by the characterizing features of claim 1. Accordingly, a method for operating an RFID system in which a reading device by means of a generator at least one transponder wirelessly supplied with electromagnetic energy and in which the transponder transmits data to the reading device, in particular by modulation of its load characteristics, characterized in that for detecting Manipulations a generated by the generator for energizing the transponder generator signal and a read coil signal received by a read coil of the reader are compared by a comparison means. In this case, it is expedient that in the presence of difference components of at least one predetermined strength between the generator signal and the read coil signal, an indication signal for displaying a manipulation is output. A measure of the difference component is the different signal characteristic between the generator signal and the read coil reception signal.

Technically, the problem is solved in a reader of the type mentioned by the characterizing features of claim 8. Accordingly, a reader for an RFID system, comprising a resonant circuit with a transmit / read coil for transmitting and receiving electromagnetic signals and a generator coupled to the resonant circuit for exciting the resonant circuit with a generator signal, characterized by a with the read coil and with the generator coupled comparison means adapted to compare the generator signal and a read coil signal received by the read coil. Advantageously, means are provided for outputting a display signal for indicating a manipulation when there are differential portions of at least one predetermined strength between the generator signal and the read coil signal.

In an RFID system of the type mentioned, the object is achieved by the characterizing feature of claim 15. Accordingly, an RFID system having at least one reading device and a number of transponders, which are supplied with electromagnetic energy by the reading device and designed to transmit data to the reading device, in particular by load modulation, is characterized in that the at least one reading device is an inventive device Reader is formed.

According to the invention, therefore, the presence of a foreign energy source, which is superimposed on the electromagnetic field of the reader, recognized by difference shares between a generator signal of the reader and a read pulse signal received by the reader and evaluated as an indication of a possible manipulation attempt. Without a foreign signal source, the comparison means detects no difference components, since the generator signal and the read coil signal are the same. Since the read coil signal in the case of manipulation contains both inherent shares generated by the generator and foreign components fed by the attacker, it will alternatively be referred to below as a mixed signal.

Advantageous developments of the invention are the subject of dependent claims. Thus, in a further development of the method according to the invention for achieving a distinguishability between the generator and a foreign energy source, it is provided to make the sources distinguishable by providing the intrinsic component of the field energy of the reading device with a signature via a suitable modulation. For this purpose, it may be provided in the course of an embodiment of the method according to the invention that the reading device intercepts a frequency of the generator signal, wherein the key can be repeated in particular.

A corresponding development of the reader according to the invention provides that this has a Umtastmittel for keying a frequency of the generator signal.

Alternatively and / or additionally, in the course of a further embodiment of the method according to the invention, a phase position of the generator signal (repeatedly) can be keyed. Accordingly, the reading device according to the invention is characterized in a further development by a Umtastmittel for keying a phase of the generator signal.

In order to avoid that an attacker detects the Umtastung the generator signal and readjusting his jammer according to the new properties of the generator signal is provided in a further development of the method that the Umtast the frequency and / or the phase angle is carried out according to a predetermined pattern. In other words, there is a variable time sequence of Changes in different amounts of the phase angle or the frequency of the generator.

In order to further complicate the mentioned readjustment of the control transmitter, the predetermined pattern in the course of a further embodiment of the method according to the invention can be a pseudo-random code.

In this way, it is the attacker for technical reasons, at least for a short time after the key is not possible to eliminate existing difference components between the read coil signal / mixed signal and the generator signal, so that the manipulation attempt remains recognizable. Therefore, a development of the method according to the invention provides that the given pattern is a pseudo-random code. In particular, the evaluation time is selected such that it is shorter than a time required for eliminating the difference components (eg, by suitable regulation).

Corresponding developments of the reader according to the invention provide that the Umtastmittel is designed for repeated keying of the generator signal, wherein the Umtastmittel can be designed in particular for keying the generator signal according to a predetermined pattern. Advantageously, the predetermined pattern in development of the reader according to the invention is a pseudo-random pattern.

Fig. 1

ein schematisches Blockdiagramm eines erfindungs-gemäßen RFID-Systems und

Fig. 2

ein detaillierteres Schaltschema eines Lesegeräts in dem RFID-System gemäß Fig. 1.

Further advantages and features of the present invention will become apparent from the following description of exemplary embodiments with reference to the drawing. It shows:

Fig. 1

a schematic block diagram of an inventive RFID system and

Fig. 2

a more detailed circuit diagram of a reader in the RFID system of FIG. 1.

1 schematically shows an RFID system 1 with a reading device 2 and at least one transponder or tag 3. Furthermore, a jammer 4 is shown in FIG. 1, but as such is not part of the RFID system 1.

The reader 2 and the transponder 3 are, as shown in Fig. 1 by means of a double arrow EDA, for the purpose of supplying energy to the transponder 3 and for data exchange via electromagnetic fields in operative connection. In general, the transponder 3 is supplied with energy via electromagnetic fields emitted by the reader 2 and reaches via a targeted change of at least one property of these fields, in particular by load modulation, a transmission of user data, such as an identification number, back to the reader 2. The reader detects a Signature of this modulation and wins from it the transmitted user data.

The jamming transmitter 4 is an active manipulator which attempts to generate a sufficiently high field strength by means of a transmitted interference signal SS at the reading device 2 in order to dominate the above-described effect of the transponder 3 so that its modulation signature by the reading device 2 is no longer present is recognized. Since the jammer 4 is an active unit (as opposed to the passive transponder 3), by generating a high field strength, it is generally capable of coupling the transponder 3 to the reader 2 despite a possibly larger distance between jammer 4 and reader 2 to dominate. In this way, an attacker operating the jammer 4 can hide the presence of the transponder 3 with respect to the reader 2. Moreover, it is a suitable modulation of a power of the jammer. 4 also possible to simulate the reader 2 a fake reading information (manipulated user data).

2 shows a more detailed circuit diagram of the reader 2 in the RFID system 1 of FIG. 1. The reading device 2 has a resonant circuit 5 formed by an inductance L and a capacitance C. It is connected to a generator 7 via a decoupling element 6. which generates an electrical alternating voltage. The generator 7 is in operative connection with a Umtastmittel 8. Parallel to the decoupling member 6 and the generator 7, a data evaluation unit 9 is connected. In addition, the reading device 2 has a comparison means 10, whose first input 10.1 is connected to the inductance L of the resonant circuit 5 and whose second input 10.2 is connected to the generator 7.

Furthermore, the reading device 2 according to FIG. 2 also has an ammeter 11 for determining a load current I and a voltmeter 12 for determining a resonance voltage U at the oscillating circuit 5.

The generator 7 generates an alternating electrical voltage, which is supplied to the resonant circuit 5 via the decoupling member 6. Generator and resonant circuit frequency are at least near the resonance. The quality of the resonant circuit is dimensioned such that the frequency of the generator remains within the bandwidth despite, for example, caused by metallic objects changes in the resonant frequency of the resonant circuit. The decoupling member 6 is required in order to influence or minimize the reaction of the generator 7 to the resonant circuit 5. By means of the current meter 11 and / or the voltmeter 12, changes caused by the transponder 3 (FIG. 1), such as a change in the load current I or the resonance voltage U at the oscillating circuit 5, can be determined. Accordingly, by the evaluation unit 9, a signature of the transponder. 3 (Fig. 1) detected and a corresponding payload can be obtained.

It should be noted that in a practical embodiment of the reader 2 according to FIG. 2, the ammeter 11 and the voltmeter 12 do not have to exist as structural units separate from the evaluation unit 9. In the present case, in particular, the voltmeter 12 may also be integrated into the evaluation unit 9, so that it includes changes in the resonance voltages on the resonant circuit 5 to the signature of the transponder 3 (FIG. 1), as explained above.

Now, if an attacker uses the jammer 4 shown in FIG. 1 to supply the RFID system 1 with external energy, it is possible according to the invention to detect the presence of the energy source which is superimposed on the electromagnetic field of the reading device and thus a potential manipulation attempt. For this purpose, a mixed signal MS, which represents the sum of signal components of the foreign source (jammer 4, FIG. 1) and of the generator 7, is supplied to the first input 10.1 of the comparison means 10 designed as discriminator in the course of the present example. At the same time, the second input 10. 2 of the comparison means 10 is supplied with a generator signal GS generated directly by the generator 7. The comparison means 10 compares the signals present at the inputs 10.1, 10.2 with respect to whether they differ in their frequency and / or phase position. With corresponding differences, differential or mixed products such as beating arise. Thus, if there are differential portions of at least one predetermined magnitude between the generator signal GS and the mixed signal MS or read coil signal supplied by the inductance L, the comparison means 10 generates an indication signal AS which is output to indicate possible manipulation or otherwise as a control signal for triggering a response to the signal Manipulation attempt can be used.

However, there is a possibility that an attacker attempts to synchronize his jammer 4 (FIG. 1) with the generator signal GS, where z. B. a phase locked loop (PLL) can be used. In order to reliably detect a manipulation attempt of the RFID system in this case, the Umtastmittel 8 causes a Umtastung the frequency and / or phase of the generator 7 and the generator signal GS, the frequency shift keying within such limits to the resonant frequency of the resonant circuit 5 so that the communication between reader 2 and transponder 3 (FIG. 1) is not impaired in principle.

After the generator signal GS has been keyed over, the attacker or the jamming transmitter 4 (FIG. 1) requires a finite time for readjustment of the interference signal, for example due to a transient of the PLL, before the interference signal SS (FIG. 1) synchronizes with the generator signal GS is. During this time, in the mixed signal MS, the said difference parts compared to the generator signal are present, which are detected by the comparison means 10, as described above.

In particular, it is possible in this connection to specify a specific maximum comparison or evaluation time for the comparison in the comparison means 10, within which the comparison of the generator signal GS and the mixed signal MS should take place after the key has been keyed in order to readjust the jammer 4 (FIG ) exclude.

In order to further prevent an attacker from reversing his jammer time parallel to the generator 7 of the reader 2 and thus again eliminates the difference portions of the composite signal MS, is further provided according to the embodiment of Fig. 2, that the keying of the generator 7 and the generator signal GS is performed by the Umtastmittel 8 in the context of a (pseudo) random sequence. With In other words, the Umtastmittel 8 causes a Umtastung the generator signal GS not at regular, repetitive intervals, but quasi-random, so that the attacker who does not know this pseudo-random sequence, the jammer 4 (Fig. 1) can not time-parallel to the reader 2 ,

Due to the described technical characteristics of a PLL or a comparable control circuit that can be used in the jammer 4, this always results in a certain time window within each of which differential components between the generator signal GS and the mixed signal MS can be detected by the comparison means 10. Only without a foreign signal source, the comparison means 10 detects no difference shares, since the generator signal GS and read coil signal (mixed signal MS) are identical, which corresponds to an undisturbed operation of the RFID system 1 (Fig. 1).

In summary, the fact that the attacker must supply the system with external energy is used to expose the manipulation attempt. To ensure the distinctness of external energy of the jammer and the self-field energy of the reader, the intrinsic portion of the field energy of the reader can be provided with a signature by a suitable modulation, as described in detail above. This will detect the presence of a foreign energy source.

The proposed approach according to the invention is characterized by particular economy, since to increase the security of the RFID system only a (one-time) effort to adapt the reader, possibly a corresponding additional device, is necessary. On the side of the mass produced and in large numbers produced transponder no additional costs.

Claims (15)

Method for operating an RFID system (1), in which a reading device (2) supplies at least one transponder (3) wirelessly with electromagnetic energy by means of a generator (7) and in which the transponder (3) transmits data to the reading device (2) transmits, in particular by modulating its load characteristics, characterized in that for detecting manipulations by the generator (7) for exciting the transponder (3) generated generator signal (GS) and by a read coil (L) of the reader (2) received read coil signal (MS) are compared by a comparison means (10). A method according to claim 1, characterized in that in the presence of difference portions of at least one predetermined strength between the generator signal (GS) and read coil signal (MS), an indication signal (AS) is output for displaying a manipulation. A method according to claim 1 or 2, characterized in that the reading device (2) a frequency of the generator signal (GS) umtastet. Method according to one of claims 1 to 3, characterized in that the reading device (2) reverses a phase position of the generator signal (GS). A method according to claim 3 or 4, characterized in that the Umtasten the frequency and / or phase angle is carried out according to a predetermined pattern. A method according to claim 5, characterized in that the predetermined pattern is a pseudo-random code. Method according to one of claims 1 to 6, characterized in that the comparison of the generator signal (GS) and read coil signal (MS) is evaluated during a time interval, in particular after a successful rescanning, which is shorter than a predetermined evaluation time. A reader (2) for an RFID system (1), comprising a resonant circuit (5) with a transmit / read coil (L) for transmitting and receiving electromagnetic signals and a generator (7) coupled to the resonant circuit (5) for exciting the Oscillator circuit (5) having a generator signal (GS), characterized by a comparison means (10) coupled to the read coil (L) and to the generator (7) and for comparing the generator signal (GS) and a read coil signal (MS) received by the read coil ) is trained. A reader according to claim 8, characterized in that means are provided for outputting a display signal (AS) for indicating a manipulation, when between the generator signal (GS) and read coil signal (MS) difference portions of at least one predetermined strength are present. Reader (2) according to claim 8 or 9, characterized by a Umtastmittel (8) for keying a frequency of the generator signal (GS). Reader (2) according to one of claims 8 to 10, characterized by a Umtastmittel (8) for keying a phase of the generator signal (GS). Reader (2) according to claim 10 or 11, characterized in that the Umtastmittel (8) for repeated keying of the generator signal (GS) is formed. Reader (2) according to one of claims 10 to 12, characterized in that the Umtastmittel (8) for keying the Generator signal (GS) is formed according to a predetermined pattern. Reader (2) according to any one of claims 10 to 13, characterized in that the Umtastmittel (8) for keying the generator signal (GS) is designed according to a pseudo random pattern. RFID system (1) with at least one reading device (2) and a number of transponders (3) which supplies electromagnetic energy through the reading device (2) and is designed to transmit data, in particular by load modulation, to the reading device (2) are characterized in that the at least one reading device (2) is designed according to one of claims 7 to 12.

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